An Organic Light emitting Diode (OLED) display is one of the focuses in the research field of flat panel displays at present. OLED has lower power consumption, a lower production cost, self-illuminating, a wider angle of view, a higher response speed, and other advantages as compared with a Liquid Crystal Display (LCD). At present, the OLED displays have taken the place of the traditional LCD displays in the flat panel display fields of a mobile phone, a Personal Digital Assistant (PDA), a digital camera, etc., where the design of a pixel circuit is a core technology of the OLED display, and a research thereon is of great significance.